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[mpl] Nested Scopes w/Placeholders
by Kitten, Nicholas 06 Feb '12

06 Feb '12

I've recently been doing a lot mpl::folding (in boost 1.47), and I was disappointed when I realized that a nested fold wouldn't work with a lambda expression passed to the inner call, as in this example which extracts elements of sequences: using namespace mpl; using namespace mpl::placeholders; typedef vector< vector<char>, vector<int> > vec_of_vecs; typedef vector< char, int > expected_result; typedef fold< vec_of_vecs, vector<>, fold< _2, _1, *push_back< _1, _2 >* // wrong - refers to outer arguments > >::type result; BOOST_MPL_ASSERT(( equal<result, expected_result> )); After looking around for a solution I came across an old thread<http://lists.boost.org/boost-users/2004/12/9269.php> on the same subject, where it was suggested using mpl::protect might work. Indeed, the following modification does what I want, without any changes to the library: typedef fold< vec_of_vecs, vector<>, fold< _2, _1, *protect< lambda< push_back< _1, _2 > >::type >* // correct > >::type result; Of course, this is a little on the verbose side. In the old thread, Daniel Wallin suggested suggested changing the definition of lambda to yield syntax more in line with the runtime version of boost::bind, but that would apparently break other code. What about instead adding a specialization to protect for placeholder expressions? Indeed, the source in protect.hpp seems to indicate such a thing might've been in the works at one point, but I didn't see any more references to it: template< typename BOOST_MPL_AUX_NA_PARAM(T) * , int not_le_ = 0 // not lambda expression?* > struct protect : T { ... typedef protect type; }; What about changing it to something like this? template< typename BOOST_MPL_AUX_NA_PARAM(T) * , typename not_le_ = typename is_lambda_expression< T >::type* > struct protect : T { ... typedef protect type; }; *template< typename T >* *struct protect< T, mpl::true_ > : lambda<T>* *{* *...* *typedef protect type;* *};* Doing so would remove the inner lambda<...>::type expression, yielding the expected syntax. Could that be done without messing up everything else? Thanks, *Nick Kitten* Software Engineer Center for Video Understanding Excellence ObjectVideo, Inc.

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[gsoc] Summer of Code 2012
by Andrew Sutton 05 Feb '12

05 Feb '12

Has it been a year already? Google has just announced the 2012 Summer of Code program, and we'd like to participate again. I think last year was particularly successful. We reviewed and accepted two new libraries and moved several more into a state where they can be reviewed. This year should be interesting. We have a new C++ programming language, several libraries in the standard, and we want more. Many, many more. If you didn't get a chance to watch Herb Sutter's keynote talk at GoingNative 2012, you should. It will be available on-demand from this site some time in the next few days. http://channel9.msdn.com/Events/GoingNative/GoingNative-2012 [Spoiler alert] Herb wants libraries -- and not just tools for programmers. C++ wants UI libraries, graphics, database connectivity, cryptography, XML, network protocols, SMS support, back office support, etc. I would love to see some of these libraries developed through Boost. In C++11. Bjarne Stroustrup said he hadn't seen this much energy around C++ in a decade. People are excited to be writing C++11 -- and they're younger people for the first time in a long time. We should be capitalizing on this. If you have library ideas, please email me here: andrew.n.sutton -at- gmail.com. I will collect these and put them on the idea page. Some comments for mentors: I'm not concerned with summer-long time constraints this year. I'd really like to establish long-term relationships with our students. I'm not strictly concerned with backwards compatibility support. I think we should be encouraging students (and people in general) to write in C++. Hiding new language features behind compatibility macros isn't exciting. It might be fine for when time comes for releases, but let's not require students to build release-ready software. This year, I'd like to see proposals for *new* libraries to be written in C++11. Andrew

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[bgl] Maximum Adjacency Search
by Fernando Vilas 04 Feb '12

04 Feb '12

Hi, Well, it took me longer than "a few days" to make time to clean up the code, but here is a patch against today's SVN-trunk. It will probably need more cleanup before it is ready, but it should be at a point where public review will help. -- Thanks, Fernando Vilas fvilas(a)iname.com

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1.49.0 Beta 1 Release Candidate
by Steve M. Robbins 04 Feb '12

04 Feb '12

Hi, I'm starting a build (using the Debian package configuration) and noticed several known bugs still present: These two bugs are patched on the trunk but not release. Can these be moved over, please? https://svn.boost.org/trac/boost/ticket/4657 https://svn.boost.org/trac/boost/ticket/6338 This issue has a simple patch that works around the problem for gcc versions prior to 4.6.3: https://svn.boost.org/trac/boost/ticket/5538 This issue has a patch that works (is used in Debian), though a jam expert could likely find a better fix: https://svn.boost.org/trac/boost/ticket/6286 Regards, -Steve (Boost maintainer for Debian)

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[random] Determining interest in Pseudo-Random Functions and Counter Based Random Number Generators
by John Salmon 03 Feb '12

03 Feb '12

I am co-author of "Parallel Random Numbers, as Easy as 1, 2, 3". which recently won the best paper award at the IEEE/ACM SC'11 conference. I'm also co-author of the related Random123 library: http://deshawresearch.com/resources_random123.html My colleagues and I would like to contribute a similar library to Boost as well. This isn't just a "port" of the Random123 library. Boost's focus on C++ allows for both simplification and clarification of the ideas in the paper and the original library. I've done a preliminary draft of some code that fits nicely into the existing Boost Random library. It's incomplete, but I think there's enough for folks to look at and gauge further interest. A zip file with a boost-like layout is here: http://thesalmons.org/john/random123/prf_boost/prf_boost.zip The README from the zip file is appended. I look forward to your comments and suggestions. John Salmon -------------- README ------------------- This extension of the Boost Random library adds "Pseudo-Random Functions" (PRFs) as an alternative to conventional "Uniform Random Number Generators" and "Random Number Engines". It is an incomplete draft, intended to start a conversation. It is not ready-to-use library. The case for using PRFs in Monte Carlo and statistical simulation is given in the paper, "Parallel Random Numbers -- As Easy as 1, 2, 3", by Salmon, Moraes, Dror & Shaw, in the Proceedings of SC'11: http://dl.acm.org/citation.cfm?doid=2063405 also available at http://www.thesalmons.org/john/random123/papers/random123sc11.pdf PRFs have been known for many years, but either their advantages were unrecognized or they were thought to have poor performance with respect to conventional URNGs. The paper shows that PRFs exist with excellent statistical properties, and highly desirable space and time characteristics. Also, note that the terminology in the paper, is slightly different from that used here. In the paper they're called "Counter Based Random Number Generators". PRFs are well-known in cryptography, but the PRFs here (except for AES) are *not* cryptographically strong. Nevertheless, they have satisfied extensive tests of statistical quality and should satisfy the needs of Monte Carlo simulation and other fields that routinely use random numbers. PRFs are pure functions (functors in C++) with the property that they return "random" values, even when presented with highly regular inputs (see the paper for a discussion of how randomness is empirically established). The user of a PRF assembles the input, calls the function and obtains a "random" result which can then be used in the same way as a value obtained from a conventional URNG or Engine. In contrast, a conventional Random Number Engine has a much more limited API: the caller is restricted to seeding the engine, once and for all, and then repeatedly asking for the "next" random value. PRFs eliminate the sequential dependence inherent in conventional RNGs. With a PRF, one can compute the "n-th" value in O(1) time, without stepping through earlier values. In fact, with a PRF, the notion of an "n-th" value loses its significance. One simply obtains a random value. Eliminating sequential dependence can be especially useful for parallel, multi-threaded applications. For example, one can assemble a PRF's input from application-level data, e.g., object id, voxel number, user-supplied seed value, timestep, iteration number, etc. This kind of application data is unchanged when the application is parallelized, and is generally invariant as more or fewer threads become available. The resulting random value is thus invariant to the parallelization as well. This can be enormously helpful when correctness dictates that separate "parallel" threads should use the same "random" value, or when trying to reproduce results on different platforms with different levels of parallelism. Four PRFs are implemented: threfry, philox, ars and aes, each implemented in its own header file, e.g., boost/random/ars.hpp. The file boost/random/counter_based_urng.hpp implements the counter_based_urng adapter class, which creates a Uniform Random Number Generator from a PRF, allowing programmers to use the PRF APIs together with Boost or C++1x Random Number Distributions. The file boost/random/counter_based_engine.hpp implements the counter_based_engine adapter class, which creates a Uniform Random Number Engine from a PRF, allowing PRFs to be used with software that relies on the Uniform Random Engine concept. For better or worse, wrapping a PRF in a counter_based_engine adapter completely obscures the PRF's API and reintroduces sequential dependence. The zip file also contains a copy of the candidate Boost Endian library copied from boost sandbox. Endian-swapping is required by the AES engine on bigendian machines, and the library meets our needs. Concepts -------- All PRFs have a domain_type and a range_type and with d a "permissible" object of the domain type, the expression: prf(d) is of the range_type. In many cases, every possible value of domain_type will be "permissible", but we leave open the possibility that the prf may place restrictions on the values of domain_type that produce "random" results. The values returned by the prf should be "random", a concept that is difficult to make both precise and achievable. Roughly, for most sequences, including highly "regular" sequences, of distinct, permissible domain_type values, d1, d2, d3, ..., the sequence: prf(d1), prf(d2), prf(d3), ... is statistically indistinguishable from a sequence of independent, uniformly distributed random variables sampling the range_type. In most cases, the output of the prf will uniformly sample all possible values of the range_type, but we leave open the possibility that it may only sample a subset and that the output is only uniform over the subset. Keyable PRFs have a key_type, a corresponding constructor, and setkey() and getkey() member functions. Keyable PRFs constructed with different keys must also be statistically independent. I.e., even for highly regular sequences of distinct (key, domain) pairs: (k1, d1), (k2,d2), ... the sequence: Prf(k1)(d1), Prf(k2)(d2), ... is statistically indistinguishable from a sequence of independent random uniformly distributed samples of the range_type Keyable PRFs may also be Seedable in which case they also have seed() member functions and corresponding constructors similar to those of Random Number Engines. Seeding a PRF is equivalent to setting its key to some value corresponding to the output of sseq.generate(). A PRF has a Countable Domain if its domain_type has member functions begin(), end(), and back() with semantics identical to that of boost::array<Uint, N> for some unsigned integral type Uint and some N. It must also have member functions domain_array_min() and domain_array_max() that specify the permissible domain values. Any array, da, whose members, da[i], satisfy: prf.domain_array_min() <= da[i] <= prf.domain_array_max[] must be "permissible". A PRF has an Integer Array Range if its range_type has member functions begin(), end(), and size() with semantics identical to boost::array<RangeInt, N>, for some integral type, RangeInt and constant N. It must also have static constexpr member functions, range_array_min() and range_array_max() that specify the subset of range values sampled by the PRF. For any sequence of permissible domain value, d1, d2, ..., the integers: prf(d1)[i], prf(d2)[i] must be statistically indistinguishable from independent uniformly distributed RangeInts from range_array_min() up to and including range_array_max(). If a PRF has a Countable Domain and an Integer Array Range, then: counter_based_urng<Prf> satisfies the requirements of a Uniform Random Number Generator. If, in addition, the PRF is Seedable, Streamable and Equality Comparable, then: counter_based_engine<Prf> satisfies the requirements of a Random Number Engine. A PRF is a Pseudo-Random Bijection if it is one-to-one and onto. I.e., if it has an inverse. It is not necessary for the inverse to have a practical implementation. It is sufficient that the inverse exist mathematically. A PRF is a Pseudo-Random Permutation if it is a Bijection and its domain_type is the same as its range_type. The four implemented PRFs are CopyAssignable, EqualityComparable, Streamable, Keyable, Seedable, Pseudo-Random Permutations with Integer Array ranges and Countable domains. Hence, they satisfy the requirements of counter_based_engine and counter_based_urng. Differences from Random123 -------------------------- This code is inspired by the Random123 library, but there are significant differences. New terminology: threefry<2, uint64_t> is a "Pseudo-Random Function" (PRF). PRFs take a key_type as a constructor argument, and are bijections on their ctr_type. Thus, instead of: typedef r123::Threefry2x64 r123_t; r123_t::ctr_type c; r123_t::key_type k r123_t::ctr_type r = r123_t(c, k) You now say: typedef boost::random::threefry<2, uint64_t> prf_t; prf_t::key_type k; prf_t myprf(k); prf_t::domain_type c; prf_t::range_type r = myprf(c); // Or alternatively, (more reminiscent of Random123) prf_t::range_type r2 = prf_t(k)(c); AESNI ----- Use of AESNI is tricky because we want both compile-time and runtime control over whether AESNI is used. The compile-time control is determined by BOOST_HAS_AESNI, which we assume will be set by some config file based on compiler-specific symbols (__AES__, __x86_64__, __ICC, __GNUC__) and possible user-overrides. But even if AESNI support is compiled in, we have to detect it and fall back to a software implementation at runtime if it's not available. The check requires either an asm with GCC-compatible compilers or an intrinsic with MSVC-compatible compilers. Endianness is another complication. The AESNI implementation only works on x86_64 platforms, so it is not endian-sensitive. In fact, it *defines* how multi-byte quantities are to be interpreted. In contrast, the software implementation has to be endian-aware. The current implementation has not been tested with other endians, and hence is almost certainly broken. And finally, the AESNI intrinsics are *very* fast. We don't want to weigh them down with lots of runtime checks. With AESNI enabled, the runtime overhead should cost no more than a single conditional at the top of operator()(c). The choice between hardware and software AES is controlled by a member data field, useAESNI, of the prf class. If hw AES is compiled in, useAESNI is initialized by a runtime check of the CPU capabilities. It can be changed with a mutator method. If hw AES is not compiled in, useAESNI is initialized false and it is an error to try to set it to true. In detail/aes_impl.hpp, we implement two classes: detail::hw128 detail::sw128 with a common interface that minimally meets the needs of AES and ARS. The interface includes +=, ^= constructors from array<uintW, N>, aesenc, and aeskeygenassist primitives, etc. The crucial functions in AES and ARS are then written with a template parameter that is assumed to provide the interface. An idiom like: #if BOOST_HAS_AESNI if( useAESNI ) method<detail::hw128>(args); else #endif method<detail::sw128>(args); gives the desired compile-time and runtime control.

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Use macro varargs within BOOST_NOEXCEPT_IF
by Daryle Walker 03 Feb '12

03 Feb '12

I was going to ask about adding a BOOST_NOEXCEPT, but I just checked that the trunk already has it: //---#ifdef BOOST_NO_NOEXCEPT# define BOOST_NOEXCEPT# define BOOST_NOEXCEPT_IF(Predicate)# define BOOST_NOEXCEPT_EXPR(Expression) false#else# define BOOST_NOEXCEPT noexcept# define BOOST_NOEXCEPT_IF(Predicate) noexcept((Predicate))# define BOOST_NOEXCEPT_EXPR(Expression) noexcept((Expression))#endif//--- If the compiler supports varargs in macros, should we have: //===# define BOOST_NOEXCEPT_IF(...) noexcept(__VA_ARGS__)# define BOOST_NOEXCEPT_EXPR(...) noexcept(__VA_ARGS__)//=== (I think that's the right syntax.) instead so comma expressions can be used within a noexcept without the extra parentheses? But I doubt that it makes a difference here, since anything within the noexcept must be interpretable as a single expression. (I think it does for decltype, though. Extra parentheses turn a value type into a reference type(?).) Daryle W.

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[metagraph]
by Kitten, Nicholas 03 Feb '12

03 Feb '12

Hi Gordon (and whoever else is involved), What's the current status of metagraph / mpl_graph? I've been using msm::mpl_graph for error-checking/scheduling in a compile-time filter graph framework (similar to state machines, but focus is on data flow), and I'd certainly like to see more. As is, I've already implemented a topological sort based on the BFS which doesn't yield errors on cyclic graphs (which I'd be happy to contribute if you don't already have one), and I have some thoughts on improvement. I saw the BoostCon slides and the current state of the sandbox, and I was wondering if there's more code lurking out there somewhere, unchecked-in. Anyway, the single biggest flaw I see with the current BFS and DFS (and the BGL models they're based on) is that there is no way for the user to specify a termination condition in the base algorithm. It seems silly that an algorithm called "Search" can't end without traversing the whole connected component! Indeed, if there were simply an optional predicate determining whether a candidate vertex should be added to the stack/queue, I wouldn't have needed to write a separate algorithm for topo sort. The other thing is that not all of the listed visitor operations are called in the current implementations. Adding things like "initialize_vertex" and "non_tree_edge" to BFS is an easy fix. Thanks, Nick Kitten Software Engineer Center for Video Understanding Excellence ObjectVideo, Inc. http://www.objectvideo.com

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[range] Performance benchmarks?
by Beman Dawes 02 Feb '12

02 Feb '12

A question came up in a long bikeshed discussion on a C++ committee mailing list as to the performance of range based interface versus a begin/end iterator interface (I.E. traditional STL interface) to the same algorithms. Out of curiosity, I checked the Boost.Range docs, but didn't see any performance measurements. It might encourage potential users to take the leap if the Boost.Range "Introduction" page made some mention of performance implications for use of the Boost library. The intro gives a "Push the even values from a map in reverse order into the container target" example: // Assume that is_even is a predicate that has been implemented elsewhere... push_back(target, my_map | map_values | filtered(is_even()) | reversed); Are there any benchmarks available for this? What does the straight STL version of the code look like? --Beman

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[1.49] No description about Boost.Heap in Library Documentation page
by Michel Morin 02 Feb '12

02 Feb '12

There is no description about Boost.Heap at http://www.boost.org/doc/libs/1_49_0_beta1/ Ditto for "trunk/boost/libs/libraries.htm" Regards, Michel

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[1.49.0] New libraries in 1.49.0?
by Beman Dawes 02 Feb '12

02 Feb '12

What are the new libraries in 1.49.0? --Thanks, --Beman

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